PERCOLATION and PINNING in SUPERCONDUCTING MgB2 in RELATION
to Nb-, NbN,- and HTS-SUPERCONDUCTORS
•Juergen Halbritter
Forschungszentrum Karlsruhe, Institut fuer Materialforschung I, Postfach
3640, 76021 Karlsruhe, Germany
The hindrance of electric transport by grain/island boundaries in distances
aJ( £ 1mm)
is well accepted in the normal conducting state, whereas related critical
Josephson current densities jcJ are less well known. For a quantitative
model the resistivity [1]
| r(T) = Rbn/aJ
+ p(ri(T) + ri(0)) |
|
(\theequation) |
is fitted to observations yielding boundary resistances Rbn(Wcm2),
residual resistances by scattering in the grains ri(0)
and percolation factors p > 1 by current diverting
boundaries with Rbn ³ mWcm2.
Like in the case of HTS where for critical current densities jc(H
< Hc1) @ jcJ(H)
holds by Josephson fluxon pinning with jcJRbn2
@ 10-12 VWcm2
in MgB2 jcJRbn @
D/e fit the data. Relevant tunnel and scattering
processes will be discussed.
\lbrack 1 \rbrack J. Halbritter, Phys. Rev. B 48, 9735 (1993) and Supercond.
Sci. Technol. 12, 883 (1999).